Investigation into methods of generating digital waveforms have been under way for some time. In particular, it is conventional practice to employ a voltage controlled oscillator (VCO) to generate such a waveform. Referring now to FIG. 1, a prior art voltage controlled oscillator 10 is shown. Oscillator 10 is constructed by connecting an odd number of inverters 12 in series into a loop to form oscillator 10. As shown in FIG. 2, when the voltage at node a goes from a logic low to a logic high, node b transitions from a logic high to a logic low state after a time delay of d. Similarly, the above-described transition will cause node c to transition from a logic low to a logic high after a time delay of d. This structure is conventionally known as a ring oscillator, and its output is taken with reference to node a. Thus, the output frequency of the oscillator 10 is the same as the oscillating frequency of any of the individual inverters 12 in the loop. It should be appreciated that when such a structure is constructed using CMOS devices, sudden surges of power consumption are observed at every gate transition (i.e., from a logic low to a logic high, or, from a logic high to a logic low). Therefore, oscillator 10 results in high-frequency harmonic noise on the power source line. For example, oscillator 10 has an output frequency of f.sub.VCO =1/(6d), where d is the time delay associated with inverter 12, which may, for example, be 10 nanoseconds. However, transitions occur every d seconds generating a harmonic having a frequency of three times the output frequency (i.e., f.sub.VCO =1/2d). This odd high-frequency harmonic noise on the power source line is undesirable.
Furthermore, since the loop frequency and the oscillator output frequency are the same, the output frequency is limited by the number of inverters used. Moreover, the output frequency of oscillator 10 is limited by the delay time d associated with individual inverters 12 such that the maximum frequency, f.sub.max, is equal to 1/2md, where m is the number of inverter elements used.
The present invention is directed to overcoming one or more of the problems as set forth above.